As the demand for integrated circuits with ever-shrinking device features continues to increase, the need for improved illumination sources used for inspection of these ever-shrinking devices continues to grow. One such illumination source includes a laser-sustained plasma source. Laser-sustained plasma light sources (LSPs) are capable of producing high-power broadband light. Laser-sustained light sources operate by focusing laser radiation into a gas volume in order to excite the gas, such as argon, xenon, mercury and the like, into a plasma state, which is capable of emitting light. This effect is typically referred to as “pumping” the plasma. In order to contain the gas used to generate the plasma, an implementing plasma cell requires a “bulb,” which is configured to contain the gas species as well as the generated plasma.
A typical laser sustained plasma light source may be maintained utilizing an infrared laser pump having a beam power on the order of several kilowatts. The laser beam from the given laser-based illumination source is then focused into a volume of a low or medium pressure gas in a plasma cell. The absorption of laser power by the plasma then generates and sustains the plasma (e.g., 12K-14K plasma).
Traditional plasma bulbs of laser sustained light sources are formed from fused silica glass. Fused silica glass absorbs light at wavelengths shorter than approximately 170 nm. The absorption of light at these small wavelengths leads to rapid damage of the plasma bulb, which in turn reduces optical transmission of light in the 190-260 nm range. Absorption of short wavelength light (e.g., vacuum UV light) also stresses the plasma bulb, which leads to overheating and potential bulb explosion, limiting the use of high power laser-sustained plasma light source in effected ranges. Therefore, it would be desirable to provide a plasma cell that corrects the deficiencies identified in the prior art.